The present invention relates to a pressure-resistant helical corrugated pipe mainly adapted to be buried in the ground, so that telecommunication cables such as an electric cable and a telephone cable can be installed in such a corrugated pipe for the purpose of protecting such cables. Also, such a corrugated pipe is used as a water main pipe, a sewer pipe, or a liquid transport pipe used in a plant or a factory.
Among such conventional pressure-resistant helical corrugated pipes, the type of corrugated pipes adapted for underground use have been required to be pressure-resistant in order to withstand a great ground pressure. In a conventional underground pressure-resistant pipe (see, for example, Japanese Laid-Open Utility Model Application No. 141889/86 filed by the Applicant of the present application), a continuous reinforcing belt plate made of a thin metal plate is embedded in the pipe wall and extends over the top portion of the helical corrugation, the opposite side wall portions, extending from the top portion, and part of the bottom portion.
When the metal reinforcing belt plate to be thus embedded in the pipe wall is of such a unitary configuration that this reinforcing belt plate is disposed in the top portion and opposite side wall portions of the corrugated pipe wall, with its oppositely-projecting side edge portions disposed in part of the bottom portion as described above, the pipe is excellent in pressure-resistant strength to withstand a flattening force.
Despite this, the present invention seeks to provide a pipe of the type in which a belt plate of a thin metal plate is embedded in a pipe wall to increase its pressure-resistant strength to withstand the flattening (in some cases, the metal belt plate is exposed at the surface of the pipe wall), and the pipe has a further increased pressure-resistant strength to withstand the flattening even if the belt plate material of the thin metal plate has an equal thickness, and the amount of covering synthetic resin material used in the above prior art pipe is reduced to decrease the overall weight of the pipe.